Cords such as steel cords are a preferred reinforcement material for a lot of polymer materials in a high number of different applications. It is known that the adhesion of the steel cords to the polymer material is critical to obtain an interesting composite material. For many applications, adhesion is a critical parameter determining the overall performance of the final composite material. On the other hand corrosion of the steel cord when not protected properly can be a serious problem.
Silane based coatings are known in the art to increase the adhesion between a metal filament or metal cord and a polymer material such as polyvinyl chloride, polyurethane, polyethylene terephthalate, polyacrylate, polypropylene, modified polypropylene, . . . . The silane based coatings known in the art are applied on the metal filament or metal cord by dipping the metal filament or cord in a solution comprising the silane. Alternatively, the silane based coatings known in the art may be applied on the metal filament or metal cord by painting the filament or cord with a solution comprising the silane.
Subsequently, the solvent is evaporated during the drying process and the silane based coating is cured. Finally, the metal filament or cord comprising the silane based coating is embedded in a polymer material.
The adhesion obtained between the metal and the polymer material by this type of silane based coatings is often inadequate. Numerous reasons for this inadequate adhesion can be found.
One reason is the incorrect matching between the functional groups of the silane based coating and the polymer material.
Large amounts of silane based coatings may lead to thick, inhomogeneous coatings resulting in inadequate adhesion.
Also large amounts of silane based coating present in the voids of the cord and at the interfaces between two adjacent filaments may explain the inadequate adhesion. Even after drying and/or curing the amount of silane based coatings present in the voids of the cord and at interfaces between to adjacent filaments is in many cases too high. This can result in cords having poor adhesion performance and in cords suffering from corrosion (white rust formation).
Furthermore, this type of silane based coatings often has a limited hydrolysis resistance. This may cause serious problems for example when the composite material is exposed in a humid environment.